1. Field of the Invention
A method used in a wireless communication system and related communication device are provided, and more particularly to, a method of managing multimedia broadcast multicast service (MBMS) transmission in a wireless communication system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
A multimedia broadcast multicast service (MBMS) service has been introduced in LTE specification to give the opportunity to broadcast or multicast TV, film, information such as free overnight transmission of newspaper in digital form and other media in these networks. The broadcast or multicast capability enables to reach unlimited number of users with constant network load. Further, the MBMS also enables the possibility to broadcast or multicast information simultaneously to many cellular subscribers.
Two important scenarios have identified for the MBMS service. One is single-cell broadcast, and the second is MBMS Single frequency network (MBSFN). MBSFN is envisaged for delivering services such as Mobile TV, using the LTE infrastructure. In MBSFN the transmission happens from a tightly time-synchronized set of eNBs, using the same resource block. A UE receiver will therefore observe multiple version of the signal with different delays due to the multi-cell transmission. Since the transmissions from the multiple cells are sufficiently tightly synchronized for each to arrive at the UE, this makes the MBSFN transmission appear to the UE as a transmission from a single large cell, and the UE receiver may treat the multi-cell transmission in the same way as multi-path components of a single cell transmission without incurring any additional complexity.
The MBSFN transmission takes place on dedicated subframes referred to as MBSFN subframes, which would be used for other purpose than MBMS service. For example, the MBSFN subframes can be used for data transmission between relays and the eNB or data transmission for position measurement for the UE. Namely, the MBSFN subframes may be used for non-MBMS data transmission when the MBSFN subframes are not allocated for MBMS data.
The deployment of the MBMS in the LTE system has been defined based on various configurations of geographical cell distribution, carrier frequency allocation (known as “frequency layers”) and transmission mode. A geographical area where all eNBs can be synchronized and can perform MBSFN transmission is called an MBSFN synchronization area. Within the MBSFN synchronization area, a group of cells that are coordinated for an MBSFN transmission is called an MBSFN area. Strictly speaking, one cell belongs to only one MBSFN area. Based on such “one-to-one” mapping, the UE served by that cell only read MBSFN subframe configuration associated with that MBSFN area. However, when the multiple MBSFN areas overlap, one cell may serve multiple MBSFN areas simultaneously. The UE in the overlapping area only reads one MBSFN subframe configuration (e.g. the first MBSFN subframe configuration received) in a configuration list. This causes the other MBMS service ignored.
Moreover, mappings between the MBSFN subframe configurations and multicast channel (MCH), multicast control channel (MCCH) and multicast traffic channel (MTCH) have not been described explicitly in the current LTE specification. The MCTH is a point-to-multipoint downlink channel for transmitting data traffic from the network to the UE. The MCCH is a point-to-multipoint downlink channel used for transmitting MBMS control information form the network to the UE. Both the MCCH and the MTCH are mapped to the MCH transport channel in the MBSFN operation. The MCH is used to transport user data or control message for the MBSFN operation.
In short, allocation/configuration of the MBSFN subframe and corresponding channels, e.g. MCH/MCCH/MTCH, need appropriate handling to improve MBMS resource utilization.